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The Western Carolina University team closely tracks how hurricanes affect developed coastal areas in the Southeast. Coastal geologists Blair Tormey and Katie Peek decided to compare the destruction with the FEMA flood maps after they saw an aerial video of Mexico Beach after Michael.

They looked flood risk maps and at Google Earth images to determine what the community looked like previously. The minimal-risk zone, X, represents areas where the odds of flooding would be remote, less than 0.2 percent chance of occurring in any year, or what’s commonly known as a 500-year flood. Those homes ranged from about 6 to 17 feet above sea level, Tormey said, with some as close as a lot or two away from the shoreline.

Using information from the U.S. Geological Survey, the team estimated that the storm surge in Mexico Beach must have as reached as much as 19 feet above average sea level, likely a record for Florida. Waves would have added several more feet, they said. The National Weather Service, which measures storm surge from ground level instead, has not yet confirmed its measurements.

“We saw some homes that survived,” Peek said. “They looked brand new or had deep pilings and expensive construction.”

That article had to say that FEMA maps failed to take into account global warming? Really? Let's wait for the official report on the surge. I think Jeff Lindner was over there examining the surge. If that area was built assuming a max surge of 10 ft then that was too low. An average-sized Cat 3 would produce 10-11 ft there, even though that area is not nearly as surge-prone as the MS or SE LA coasts.

whether climate change was a factor has yet to be seen, but FEMA maps don't take climate change into consideration at all as a rule. I am actually working on a project to address that and hopefully will be of some use when we finish it.

I think 19 feet is high and I'm waiting for the official report too--I recall some of that being wave heights and the actual surge is lower.

Well, the highest water mark was 21.16ft above NAVD88. This adjusts to about 20ft above MHHW, and adjusting for wave height the surge was probably below 19ft - perhaps more in the range of 15-18ft. It's really best to just wait for official numbers from NOAA.

FEMA's maps do not take sea level rise or climate change into account in any kind of quantitative way and this is pretty much intentional mapping practice. There are many reasons:

Two major ones.

- Their primary function is to establish insurance rates based on CURRENT flood risk at the time of the modelling. This is why they are called Flood Insurance Rate Maps. FEMA is not permitted by mapping guidelines to map any forward-looking risk factors such as sea level rise or more intense storms. They SHOULD be forward-looking because these maps are also used to set code requirements for floor elevations for new construction but they don't, and they aren't permitted to.

-Historical tide gauge data and calibration to past storm heights at gauged locations or high water marks are the basis for calibrating the models. Tide stations with long periods of records are used. This has the effect of minimizing to the point of near-irrelevance any upticks in storm intensities. Storms from decades ago are often used in calibrating the models. (Incidentally this same calibration issue affects flood maps on riverine watersheds where land use changes and precipitation patterns are increasing runoff but in an effort to use long-history gauge locations, the flood models may be calibrated to storms which happened decades ago prior to the land use changes.)

The linked article says that peoples homes just hundreds of feet from the Gulf were mapped in the 0.2% x zone and therefore didn't need flood insurance. In that flood zone banks do not REQUIRE flood insurance however that does not mean its not needed. Its a TRAVESTY that this zone is called the 500-year floodplain....along eroding coasts in an era of rising sea levels and with so much uncertainty in the modelling, to lead people to believe that these locations just barely above 10 feet above sea level will only flood once in 500 years is really poor risk communication.

Last edited by mitchell on Tue Nov 13, 2018 9:22 pm, edited 1 time in total.

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